ABSTRACT The goal of this R01 application is to investigate the mechanisms that drive the local activation of B cells and antibody production during chronic airway inflammation in humans. The PI has extensive training and experience in the fields of human immunology and is well equipped to carry out the proposed research plan. The PI's work that has laid the groundwork for this application indicates that B cells, antibodies, and autoantibodies, along with expression of Epstein Barr virus-induced protein 2 (EBI2), are elevated in tissue from patients with chronic rhinosinusitis (CRS), especially in a subset of patients with nasal polyps (NP). CRS affects over 30 million people in the United States and costs billions of dollars to manage and treat. Little is known about the mechanisms that drive B cell activation at mucosal sites in humans, thus this proposal represents a unique opportunity to address these important questions. Successful completion of these studies will further our understanding of regulation of mucosal B cell responses in humans and may provide the basis for investigations into novel therapeutic targets for treatment of CRS and other B cell-mediated diseases. The overarching hypothesis for this application is that the inflamed tissue microenvironment supports the local expansion and maturation of B cells, leading to overproduction of antibodies that contribute to chronic disease pathogenesis. This hypothesis will be addressed using three related but independent aims. The first aim will investigate the properties of local B cells and antibodies in NP at the single cell level. Experiments are designed to characterize the local antibody repertoire and to determine which B cell subsets contribute to local antibody production. The second aim will determine whether a specific cell type in NP, group 2 innate lymphoid cells (ILC2), activates B cells to locally produce antibodies, especially autoantibodies. Experiments are designed to assess whether ILC2s drive the maturation of B cells into plasmablasts or plasma cells and the mechanisms that facilitate this interaction. The third aim will utilize a mouse model of severe asthma to more specifically address the mechanisms involved in the interactions between B cells and ILC2. Experiments are designed to test the necessity and sufficiency of B cell-derived IL-33 in the activation of ILC2s during chronic airway inflammation, and they are directly applicable to the studies in Aims 1 and 2 of the proposal. These studies will highlight the important mechanisms that drive activation of B cells and shape the antibody repertoire during chronic inflammation in humans, and they will provide valuable insights into the mechanisms that drive B cell activation in the airways in disease. This will pave the way for future work aimed at elucidating novel targets for the design of improved therapeutic strategies to target B cells in CRS and investigating new aspects of human mucosal immune responses.